1. Field of the Invention
The present invention relates to an image forming apparatus capable of using a recording medium having a transparent portion.
2. Discussion of the Background
For an image forming apparatus used as a copier, facsimile, printer, or multi-functional device thereof, various attempts have been and are being made to obtain a glossy color image of photographic quality.
For example, a conventional image forming apparatus includes four process units serving as imaging engines to form images of, for example, yellow, magenta, cyan, and black, and additionally, another process unit having two developing devices containing white toner and transparent toner. The conventional image forming apparatus is configured as a tandem type printer, in which the process units are arranged parallel to one another.
With the conventional image forming apparatus, for example, toner images of the four colors of yellow, magenta, cyan, and black are superimposed one on top of another onto an intermediate transfer belt to form a composite color toner image thereon. Further, a white toner image and a transparent toner image are overlaid onto the composite color toner image. Consequently, the color toner image has a maximum of six toner layers.
When the color toner image is transferred onto a recording medium, a fixing device fixes the composite color toner image on the recording medium by applying heat and pressure to form a desired full-color image on the recording medium.
The base color of a recording medium may affect the tone of a finished image, degrading image quality. Alternatively, irregularities in the surface of the recording medium may degrade image quality. Hence, the conventional image forming apparatus attempts to prevent such deterioration by applying the white toner and the transparent toner as described above.
However, the conventional image forming apparatus has a cost disadvantage in that the transparent toner is applied over the entire surface of the recording medium. Moreover, differences in toner thickness between image forming areas and non-image forming areas can tax the fixing device.
In one conventional technique, a special type of recording medium is used to obtain a glossy image. Such a special recording medium has a thermoplastic resin layer on at least one face thereof. When a toner image is fixed on the recording medium in the usual manner, heat and pressure are further applied to the recording medium to obtain an image having uniform glossiness.
A conventional image forming apparatus typically includes a first fixing device and a second, specific fixing device having a very smooth belt. When the first fixing device fixes a toner image on a recording medium in the usual manner, the second fixing device melts and cools the toner image on the recording medium using the belt, thus providing an image having uniform glossiness.
However, the above-described special recording medium may need to be used together with a special fixing device to obtain such a high-gloss image. Therefore, the conventional technique may have disadvantages in terms of configuration, cost, and power consumption.